Originally Posted by
atomic sagebrush
This has been very well researched and it has been shown definitively that while there is a very slightly higher number of women with a rare and very severe form of morning sickness called hyperemesis gravidium, there is ZERO correlation between just plain morning sickness and baby's gender. and even with the HG, it is only a 3% difference so many people are getting HG with boys or girls.
Sheer speculation alert, I suspect that back in the days when people didn't have as many food choices and had little/no medical treatment for morning sickness, it is very likely that any woman with severe, or even not that severe MS, who couldn't eat enough, were probably more likely to lose an XY early on in pregnancy due to malnutrition (because XY need more nutrients from moment of conception onward) and so it might have appeared that MS = girls but it was just a weird kind of coincidence.